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ftdriver.h
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1 /***************************************************************************/
2 /* */
3 /* ftdriver.h */
4 /* */
5 /* FreeType API for controlling driver modules (specification only). */
6 /* */
7 /* Copyright 2017-2018 by */
8 /* David Turner, Robert Wilhelm, and Werner Lemberg. */
9 /* */
10 /* This file is part of the FreeType project, and may only be used, */
11 /* modified, and distributed under the terms of the FreeType project */
12 /* license, LICENSE.TXT. By continuing to use, modify, or distribute */
13 /* this file you indicate that you have read the license and */
14 /* understand and accept it fully. */
15 /* */
16 /***************************************************************************/
17 
18 
19 #ifndef FTDRIVER_H_
20 #define FTDRIVER_H_
21 
22 #include <ft2build.h>
23 #include FT_FREETYPE_H
24 #include FT_PARAMETER_TAGS_H
25 
26 #ifdef FREETYPE_H
27 #error "freetype.h of FreeType 1 has been loaded!"
28 #error "Please fix the directory search order for header files"
29 #error "so that freetype.h of FreeType 2 is found first."
30 #endif
31 
32 
34 
35 
36  /**************************************************************************
37  *
38  * @section:
39  * auto_hinter
40  *
41  * @title:
42  * The auto-hinter
43  *
44  * @abstract:
45  * Controlling the auto-hinting module.
46  *
47  * @description:
48  * While FreeType's auto-hinter doesn't expose API functions by itself,
49  * it is possible to control its behaviour with @FT_Property_Set and
50  * @FT_Property_Get. The following lists the available properties
51  * together with the necessary macros and structures.
52  *
53  * Note that the auto-hinter's module name is `autofitter' for
54  * historical reasons.
55  *
56  * Available properties are @increase-x-height, @no-stem-darkening
57  * (experimental), @darkening-parameters (experimental), @warping
58  * (experimental), @glyph-to-script-map (experimental), @fallback-script
59  * (experimental), and @default-script (experimental), as documented in
60  * the @properties section.
61  *
62  */
63 
64 
65  /**************************************************************************
66  *
67  * @section:
68  * cff_driver
69  *
70  * @title:
71  * The CFF driver
72  *
73  * @abstract:
74  * Controlling the CFF driver module.
75  *
76  * @description:
77  * While FreeType's CFF driver doesn't expose API functions by itself,
78  * it is possible to control its behaviour with @FT_Property_Set and
79  * @FT_Property_Get.
80  *
81  * The CFF driver's module name is `cff'.
82  *
83  * Available properties are @hinting-engine, @no-stem-darkening,
84  * @darkening-parameters, and @random-seed, as documented in the
85  * @properties section.
86  *
87  *
88  * *Hinting* *and* *antialiasing* *principles* *of* *the* *new* *engine*
89  *
90  * The rasterizer is positioning horizontal features (e.g., ascender
91  * height & x-height, or crossbars) on the pixel grid and minimizing the
92  * amount of antialiasing applied to them, while placing vertical
93  * features (vertical stems) on the pixel grid without hinting, thus
94  * representing the stem position and weight accurately. Sometimes the
95  * vertical stems may be only partially black. In this context,
96  * `antialiasing' means that stems are not positioned exactly on pixel
97  * borders, causing a fuzzy appearance.
98  *
99  * There are two principles behind this approach.
100  *
101  * 1) No hinting in the horizontal direction: Unlike `superhinted'
102  * TrueType, which changes glyph widths to accommodate regular
103  * inter-glyph spacing, Adobe's approach is `faithful to the design' in
104  * representing both the glyph width and the inter-glyph spacing
105  * designed for the font. This makes the screen display as close as it
106  * can be to the result one would get with infinite resolution, while
107  * preserving what is considered the key characteristics of each glyph.
108  * Note that the distances between unhinted and grid-fitted positions at
109  * small sizes are comparable to kerning values and thus would be
110  * noticeable (and distracting) while reading if hinting were applied.
111  *
112  * One of the reasons to not hint horizontally is antialiasing for LCD
113  * screens: The pixel geometry of modern displays supplies three
114  * vertical sub-pixels as the eye moves horizontally across each visible
115  * pixel. On devices where we can be certain this characteristic is
116  * present a rasterizer can take advantage of the sub-pixels to add
117  * increments of weight. In Western writing systems this turns out to
118  * be the more critical direction anyway; the weights and spacing of
119  * vertical stems (see above) are central to Armenian, Cyrillic, Greek,
120  * and Latin type designs. Even when the rasterizer uses greyscale
121  * antialiasing instead of color (a necessary compromise when one
122  * doesn't know the screen characteristics), the unhinted vertical
123  * features preserve the design's weight and spacing much better than
124  * aliased type would.
125  *
126  * 2) Alignment in the vertical direction: Weights and spacing along the
127  * y~axis are less critical; what is much more important is the visual
128  * alignment of related features (like cap-height and x-height). The
129  * sense of alignment for these is enhanced by the sharpness of grid-fit
130  * edges, while the cruder vertical resolution (full pixels instead of
131  * 1/3 pixels) is less of a problem.
132  *
133  * On the technical side, horizontal alignment zones for ascender,
134  * x-height, and other important height values (traditionally called
135  * `blue zones') as defined in the font are positioned independently,
136  * each being rounded to the nearest pixel edge, taking care of
137  * overshoot suppression at small sizes, stem darkening, and scaling.
138  *
139  * Hstems (this is, hint values defined in the font to help align
140  * horizontal features) that fall within a blue zone are said to be
141  * `captured' and are aligned to that zone. Uncaptured stems are moved
142  * in one of four ways, top edge up or down, bottom edge up or down.
143  * Unless there are conflicting hstems, the smallest movement is taken
144  * to minimize distortion.
145  *
146  */
147 
148 
149  /**************************************************************************
150  *
151  * @section:
152  * pcf_driver
153  *
154  * @title:
155  * The PCF driver
156  *
157  * @abstract:
158  * Controlling the PCF driver module.
159  *
160  * @description:
161  * While FreeType's PCF driver doesn't expose API functions by itself,
162  * it is possible to control its behaviour with @FT_Property_Set and
163  * @FT_Property_Get. Right now, there is a single property
164  * @no-long-family-names available if FreeType is compiled with
165  * PCF_CONFIG_OPTION_LONG_FAMILY_NAMES.
166  *
167  * The PCF driver's module name is `pcf'.
168  *
169  */
170 
171 
172  /**************************************************************************
173  *
174  * @section:
175  * t1_cid_driver
176  *
177  * @title:
178  * The Type 1 and CID drivers
179  *
180  * @abstract:
181  * Controlling the Type~1 and CID driver modules.
182  *
183  * @description:
184  * It is possible to control the behaviour of FreeType's Type~1 and
185  * Type~1 CID drivers with @FT_Property_Set and @FT_Property_Get.
186  *
187  * Behind the scenes, both drivers use the Adobe CFF engine for hinting;
188  * however, the used properties must be specified separately.
189  *
190  * The Type~1 driver's module name is `type1'; the CID driver's module
191  * name is `t1cid'.
192  *
193  * Available properties are @hinting-engine, @no-stem-darkening,
194  * @darkening-parameters, and @random-seed, as documented in the
195  * @properties section.
196  *
197  * Please see the @cff_driver section for more details on the new
198  * hinting engine.
199  *
200  */
201 
202 
203  /**************************************************************************
204  *
205  * @section:
206  * tt_driver
207  *
208  * @title:
209  * The TrueType driver
210  *
211  * @abstract:
212  * Controlling the TrueType driver module.
213  *
214  * @description:
215  * While FreeType's TrueType driver doesn't expose API functions by
216  * itself, it is possible to control its behaviour with @FT_Property_Set
217  * and @FT_Property_Get. The following lists the available properties
218  * together with the necessary macros and structures.
219  *
220  * The TrueType driver's module name is `truetype'.
221  *
222  * A single property @interpreter-version is available, as documented in
223  * the @properties section.
224  *
225  * We start with a list of definitions, kindly provided by Greg
226  * Hitchcock.
227  *
228  * _Bi-Level_ _Rendering_
229  *
230  * Monochromatic rendering, exclusively used in the early days of
231  * TrueType by both Apple and Microsoft. Microsoft's GDI interface
232  * supported hinting of the right-side bearing point, such that the
233  * advance width could be non-linear. Most often this was done to
234  * achieve some level of glyph symmetry. To enable reasonable
235  * performance (e.g., not having to run hinting on all glyphs just to
236  * get the widths) there was a bit in the head table indicating if the
237  * side bearing was hinted, and additional tables, `hdmx' and `LTSH', to
238  * cache hinting widths across multiple sizes and device aspect ratios.
239  *
240  * _Font_ _Smoothing_
241  *
242  * Microsoft's GDI implementation of anti-aliasing. Not traditional
243  * anti-aliasing as the outlines were hinted before the sampling. The
244  * widths matched the bi-level rendering.
245  *
246  * _ClearType_ _Rendering_
247  *
248  * Technique that uses physical subpixels to improve rendering on LCD
249  * (and other) displays. Because of the higher resolution, many methods
250  * of improving symmetry in glyphs through hinting the right-side
251  * bearing were no longer necessary. This lead to what GDI calls
252  * `natural widths' ClearType, see
253  * http://www.beatstamm.com/typography/RTRCh4.htm#Sec21. Since hinting
254  * has extra resolution, most non-linearity went away, but it is still
255  * possible for hints to change the advance widths in this mode.
256  *
257  * _ClearType_ _Compatible_ _Widths_
258  *
259  * One of the earliest challenges with ClearType was allowing the
260  * implementation in GDI to be selected without requiring all UI and
261  * documents to reflow. To address this, a compatible method of
262  * rendering ClearType was added where the font hints are executed once
263  * to determine the width in bi-level rendering, and then re-run in
264  * ClearType, with the difference in widths being absorbed in the font
265  * hints for ClearType (mostly in the white space of hints); see
266  * http://www.beatstamm.com/typography/RTRCh4.htm#Sec20. Somewhat by
267  * definition, compatible width ClearType allows for non-linear widths,
268  * but only when the bi-level version has non-linear widths.
269  *
270  * _ClearType_ _Subpixel_ _Positioning_
271  *
272  * One of the nice benefits of ClearType is the ability to more crisply
273  * display fractional widths; unfortunately, the GDI model of integer
274  * bitmaps did not support this. However, the WPF and Direct Write
275  * frameworks do support fractional widths. DWrite calls this `natural
276  * mode', not to be confused with GDI's `natural widths'. Subpixel
277  * positioning, in the current implementation of Direct Write,
278  * unfortunately does not support hinted advance widths, see
279  * http://www.beatstamm.com/typography/RTRCh4.htm#Sec22. Note that the
280  * TrueType interpreter fully allows the advance width to be adjusted in
281  * this mode, just the DWrite client will ignore those changes.
282  *
283  * _ClearType_ _Backward_ _Compatibility_
284  *
285  * This is a set of exceptions made in the TrueType interpreter to
286  * minimize hinting techniques that were problematic with the extra
287  * resolution of ClearType; see
288  * http://www.beatstamm.com/typography/RTRCh4.htm#Sec1 and
289  * https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx.
290  * This technique is not to be confused with ClearType compatible
291  * widths. ClearType backward compatibility has no direct impact on
292  * changing advance widths, but there might be an indirect impact on
293  * disabling some deltas. This could be worked around in backward
294  * compatibility mode.
295  *
296  * _Native_ _ClearType_ _Mode_
297  *
298  * (Not to be confused with `natural widths'.) This mode removes all
299  * the exceptions in the TrueType interpreter when running with
300  * ClearType. Any issues on widths would still apply, though.
301  *
302  */
303 
304 
305  /**************************************************************************
306  *
307  * @section:
308  * properties
309  *
310  * @title:
311  * Driver properties
312  *
313  * @abstract:
314  * Controlling driver modules.
315  *
316  * @description:
317  * Driver modules can be controlled by setting and unsetting properties,
318  * using the functions @FT_Property_Set and @FT_Property_Get. This
319  * section documents the available properties, together with auxiliary
320  * macros and structures.
321  *
322  */
323 
324 
325  /**************************************************************************
326  *
327  * @enum:
328  * FT_HINTING_XXX
329  *
330  * @description:
331  * A list of constants used for the @hinting-engine property to
332  * select the hinting engine for CFF, Type~1, and CID fonts.
333  *
334  * @values:
335  * FT_HINTING_FREETYPE ::
336  * Use the old FreeType hinting engine.
337  *
338  * FT_HINTING_ADOBE ::
339  * Use the hinting engine contributed by Adobe.
340  *
341  * @since:
342  * 2.9
343  *
344  */
345 #define FT_HINTING_FREETYPE 0
346 #define FT_HINTING_ADOBE 1
347 
348  /* these constants (introduced in 2.4.12) are deprecated */
349 #define FT_CFF_HINTING_FREETYPE FT_HINTING_FREETYPE
350 #define FT_CFF_HINTING_ADOBE FT_HINTING_ADOBE
351 
352 
353  /**************************************************************************
354  *
355  * @property:
356  * hinting-engine
357  *
358  * @description:
359  * Thanks to Adobe, which contributed a new hinting (and parsing)
360  * engine, an application can select between `freetype' and `adobe' if
361  * compiled with CFF_CONFIG_OPTION_OLD_ENGINE. If this configuration
362  * macro isn't defined, `hinting-engine' does nothing.
363  *
364  * The same holds for the Type~1 and CID modules if compiled with
365  * T1_CONFIG_OPTION_OLD_ENGINE.
366  *
367  * For the `cff' module, the default engine is `freetype' if
368  * CFF_CONFIG_OPTION_OLD_ENGINE is defined, and `adobe' otherwise.
369  *
370  * For both the `type1' and `t1cid' modules, the default engine is
371  * `freetype' if T1_CONFIG_OPTION_OLD_ENGINE is defined, and `adobe'
372  * otherwise.
373  *
374  * The following example code demonstrates how to select Adobe's hinting
375  * engine for the `cff' module (omitting the error handling).
376  *
377  * {
378  * FT_Library library;
379  * FT_UInt hinting_engine = FT_CFF_HINTING_ADOBE;
380  *
381  *
382  * FT_Init_FreeType( &library );
383  *
384  * FT_Property_Set( library, "cff",
385  * "hinting-engine", &hinting_engine );
386  * }
387  *
388  * @note:
389  * This property can be used with @FT_Property_Get also.
390  *
391  * This property can be set via the `FREETYPE_PROPERTIES' environment
392  * variable (using values `adobe' or `freetype').
393  *
394  * @since:
395  * 2.4.12 (for `cff' module)
396  *
397  * 2.9 (for `type1' and `t1cid' modules)
398  *
399  */
400 
401 
402  /**************************************************************************
403  *
404  * @property:
405  * no-stem-darkening
406  *
407  * @description:
408  * All glyphs that pass through the auto-hinter will be emboldened
409  * unless this property is set to TRUE. The same is true for the CFF,
410  * Type~1, and CID font modules if the `Adobe' engine is selected (which
411  * is the default).
412  *
413  * Stem darkening emboldens glyphs at smaller sizes to make them more
414  * readable on common low-DPI screens when using linear alpha blending
415  * and gamma correction, see @FT_Render_Glyph. When not using linear
416  * alpha blending and gamma correction, glyphs will appear heavy and
417  * fuzzy!
418  *
419  * Gamma correction essentially lightens fonts since shades of grey are
420  * shifted to higher pixel values (=~higher brightness) to match the
421  * original intention to the reality of our screens. The side-effect is
422  * that glyphs `thin out'. Mac OS~X and Adobe's proprietary font
423  * rendering library implement a counter-measure: stem darkening at
424  * smaller sizes where shades of gray dominate. By emboldening a glyph
425  * slightly in relation to its pixel size, individual pixels get higher
426  * coverage of filled-in outlines and are therefore `blacker'. This
427  * counteracts the `thinning out' of glyphs, making text remain readable
428  * at smaller sizes.
429  *
430  * By default, the Adobe engines for CFF, Type~1, and CID fonts darken
431  * stems at smaller sizes, regardless of hinting, to enhance contrast.
432  * Setting this property, stem darkening gets switched off.
433  *
434  * For the auto-hinter, stem-darkening is experimental currently and
435  * thus switched off by default (this is, `no-stem-darkening' is set to
436  * TRUE by default). Total consistency with the CFF driver is not
437  * achieved right now because the emboldening method differs and glyphs
438  * must be scaled down on the Y-axis to keep outline points inside their
439  * precomputed blue zones. The smaller the size (especially 9ppem and
440  * down), the higher the loss of emboldening versus the CFF driver.
441  *
442  * Note that stem darkening is never applied if @FT_LOAD_NO_SCALE is
443  * set.
444  *
445  * {
446  * FT_Library library;
447  * FT_Bool no_stem_darkening = TRUE;
448  *
449  *
450  * FT_Init_FreeType( &library );
451  *
452  * FT_Property_Set( library, "cff",
453  * "no-stem-darkening", &no_stem_darkening );
454  * }
455  *
456  * @note:
457  * This property can be used with @FT_Property_Get also.
458  *
459  * This property can be set via the `FREETYPE_PROPERTIES' environment
460  * variable (using values 1 and 0 for `on' and `off', respectively).
461  * It can also be set per face using @FT_Face_Properties with
462  * @FT_PARAM_TAG_STEM_DARKENING.
463  *
464  * @since:
465  * 2.4.12 (for `cff' module)
466  *
467  * 2.6.2 (for `autofitter' module)
468  *
469  * 2.9 (for `type1' and `t1cid' modules)
470  *
471  */
472 
473 
474  /**************************************************************************
475  *
476  * @property:
477  * darkening-parameters
478  *
479  * @description:
480  * By default, the Adobe hinting engine, as used by the CFF, Type~1, and
481  * CID font drivers, darkens stems as follows (if the
482  * `no-stem-darkening' property isn't set):
483  *
484  * {
485  * stem width <= 0.5px: darkening amount = 0.4px
486  * stem width = 1px: darkening amount = 0.275px
487  * stem width = 1.667px: darkening amount = 0.275px
488  * stem width >= 2.333px: darkening amount = 0px
489  * }
490  *
491  * and piecewise linear in-between. At configuration time, these four
492  * control points can be set with the macro
493  * `CFF_CONFIG_OPTION_DARKENING_PARAMETERS'; the CFF, Type~1, and CID
494  * drivers share these values. At runtime, the control points can be
495  * changed using the `darkening-parameters' property, as the following
496  * example demonstrates for the Type~1 driver.
497  *
498  * {
499  * FT_Library library;
500  * FT_Int darken_params[8] = { 500, 300, // x1, y1
501  * 1000, 200, // x2, y2
502  * 1500, 100, // x3, y3
503  * 2000, 0 }; // x4, y4
504  *
505  *
506  * FT_Init_FreeType( &library );
507  *
508  * FT_Property_Set( library, "type1",
509  * "darkening-parameters", darken_params );
510  * }
511  *
512  * The x~values give the stem width, and the y~values the darkening
513  * amount. The unit is 1000th of pixels. All coordinate values must be
514  * positive; the x~values must be monotonically increasing; the
515  * y~values must be monotonically decreasing and smaller than or
516  * equal to 500 (corresponding to half a pixel); the slope of each
517  * linear piece must be shallower than -1 (e.g., -.4).
518  *
519  * The auto-hinter provides this property, too, as an experimental
520  * feature. See @no-stem-darkening for more.
521  *
522  * @note:
523  * This property can be used with @FT_Property_Get also.
524  *
525  * This property can be set via the `FREETYPE_PROPERTIES' environment
526  * variable, using eight comma-separated integers without spaces. Here
527  * the above example, using `\' to break the line for readability.
528  *
529  * {
530  * FREETYPE_PROPERTIES=\
531  * type1:darkening-parameters=500,300,1000,200,1500,100,2000,0
532  * }
533  *
534  * @since:
535  * 2.5.1 (for `cff' module)
536  *
537  * 2.6.2 (for `autofitter' module)
538  *
539  * 2.9 (for `type1' and `t1cid' modules)
540  *
541  */
542 
543 
544  /**************************************************************************
545  *
546  * @property:
547  * random-seed
548  *
549  * @description:
550  * By default, the seed value for the CFF `random' operator and the
551  * similar `0 28 callothersubr pop' command for the Type~1 and CID
552  * drivers is set to a random value. However, mainly for debugging
553  * purposes, it is often necessary to use a known value as a seed so
554  * that the pseudo-random number sequences generated by `random' are
555  * repeatable.
556  *
557  * The `random-seed' property does that. Its argument is a signed 32bit
558  * integer; if the value is zero or negative, the seed given by the
559  * `intitialRandomSeed' private DICT operator in a CFF file gets used
560  * (or a default value if there is no such operator). If the value is
561  * positive, use it instead of `initialRandomSeed', which is
562  * consequently ignored.
563  *
564  * @note:
565  * This property can be set via the `FREETYPE_PROPERTIES' environment
566  * variable. It can also be set per face using @FT_Face_Properties with
567  * @FT_PARAM_TAG_RANDOM_SEED.
568  *
569  * @since:
570  * 2.8 (for `cff' module)
571  *
572  * 2.9 (for `type1' and `t1cid' modules)
573  *
574  */
575 
576 
577  /**************************************************************************
578  *
579  * @property:
580  * no-long-family-names
581  *
582  * @description:
583  * If PCF_CONFIG_OPTION_LONG_FAMILY_NAMES is active while compiling
584  * FreeType, the PCF driver constructs long family names.
585  *
586  * There are many PCF fonts just called `Fixed' which look completely
587  * different, and which have nothing to do with each other. When
588  * selecting `Fixed' in KDE or Gnome one gets results that appear rather
589  * random, the style changes often if one changes the size and one
590  * cannot select some fonts at all. The improve this situation, the PCF
591  * module prepends the foundry name (plus a space) to the family name.
592  * It also checks whether there are `wide' characters; all put together,
593  * family names like `Sony Fixed' or `Misc Fixed Wide' are constructed.
594  *
595  * If `no-long-family-names' is set, this feature gets switched off.
596  *
597  * {
598  * FT_Library library;
599  * FT_Bool no_long_family_names = TRUE;
600  *
601  *
602  * FT_Init_FreeType( &library );
603  *
604  * FT_Property_Set( library, "pcf",
605  * "no-long-family-names",
606  * &no_long_family_names );
607  * }
608  *
609  * @note:
610  * This property can be used with @FT_Property_Get also.
611  *
612  * This property can be set via the `FREETYPE_PROPERTIES' environment
613  * variable (using values 1 and 0 for `on' and `off', respectively).
614  *
615  * @since:
616  * 2.8
617  */
618 
619 
620  /**************************************************************************
621  *
622  * @enum:
623  * TT_INTERPRETER_VERSION_XXX
624  *
625  * @description:
626  * A list of constants used for the @interpreter-version property to
627  * select the hinting engine for Truetype fonts.
628  *
629  * The numeric value in the constant names represents the version
630  * number as returned by the `GETINFO' bytecode instruction.
631  *
632  * @values:
633  * TT_INTERPRETER_VERSION_35 ::
634  * Version~35 corresponds to MS rasterizer v.1.7 as used e.g. in
635  * Windows~98; only grayscale and B/W rasterizing is supported.
636  *
637  * TT_INTERPRETER_VERSION_38 ::
638  * Version~38 corresponds to MS rasterizer v.1.9; it is roughly
639  * equivalent to the hinting provided by DirectWrite ClearType (as can
640  * be found, for example, in the Internet Explorer~9 running on
641  * Windows~7). It is used in FreeType to select the `Infinality'
642  * subpixel hinting code. The code may be removed in a future
643  * version.
644  *
645  * TT_INTERPRETER_VERSION_40 ::
646  * Version~40 corresponds to MS rasterizer v.2.1; it is roughly
647  * equivalent to the hinting provided by DirectWrite ClearType (as can
648  * be found, for example, in Microsoft's Edge Browser on Windows~10).
649  * It is used in FreeType to select the `minimal' subpixel hinting
650  * code, a stripped-down and higher performance version of the
651  * `Infinality' code.
652  *
653  * @note:
654  * This property controls the behaviour of the bytecode interpreter
655  * and thus how outlines get hinted. It does *not* control how glyph
656  * get rasterized! In particular, it does not control subpixel color
657  * filtering.
658  *
659  * If FreeType has not been compiled with the configuration option
660  * TT_CONFIG_OPTION_SUBPIXEL_HINTING, selecting version~38 or~40 causes
661  * an `FT_Err_Unimplemented_Feature' error.
662  *
663  * Depending on the graphics framework, Microsoft uses different
664  * bytecode and rendering engines. As a consequence, the version
665  * numbers returned by a call to the `GETINFO' bytecode instruction are
666  * more convoluted than desired.
667  *
668  * Here are two tables that try to shed some light on the possible
669  * values for the MS rasterizer engine, together with the additional
670  * features introduced by it.
671  *
672  * {
673  * GETINFO framework version feature
674  * -------------------------------------------------------------------
675  * 3 GDI (Win 3.1), v1.0 16-bit, first version
676  * TrueImage
677  * 33 GDI (Win NT 3.1), v1.5 32-bit
678  * HP Laserjet
679  * 34 GDI (Win 95) v1.6 font smoothing,
680  * new SCANTYPE opcode
681  * 35 GDI (Win 98/2000) v1.7 (UN)SCALED_COMPONENT_OFFSET
682  * bits in composite glyphs
683  * 36 MGDI (Win CE 2) v1.6+ classic ClearType
684  * 37 GDI (XP and later), v1.8 ClearType
685  * GDI+ old (before Vista)
686  * 38 GDI+ old (Vista, Win 7), v1.9 subpixel ClearType,
687  * WPF Y-direction ClearType,
688  * additional error checking
689  * 39 DWrite (before Win 8) v2.0 subpixel ClearType flags
690  * in GETINFO opcode,
691  * bug fixes
692  * 40 GDI+ (after Win 7), v2.1 Y-direction ClearType flag
693  * DWrite (Win 8) in GETINFO opcode,
694  * Gray ClearType
695  * }
696  *
697  * The `version' field gives a rough orientation only, since some
698  * applications provided certain features much earlier (as an example,
699  * Microsoft Reader used subpixel and Y-direction ClearType already in
700  * Windows 2000). Similarly, updates to a given framework might include
701  * improved hinting support.
702  *
703  * {
704  * version sampling rendering comment
705  * x y x y
706  * --------------------------------------------------------------
707  * v1.0 normal normal B/W B/W bi-level
708  * v1.6 high high gray gray grayscale
709  * v1.8 high normal color-filter B/W (GDI) ClearType
710  * v1.9 high high color-filter gray Color ClearType
711  * v2.1 high normal gray B/W Gray ClearType
712  * v2.1 high high gray gray Gray ClearType
713  * }
714  *
715  * Color and Gray ClearType are the two available variants of
716  * `Y-direction ClearType', meaning grayscale rasterization along the
717  * Y-direction; the name used in the TrueType specification for this
718  * feature is `symmetric smoothing'. `Classic ClearType' is the
719  * original algorithm used before introducing a modified version in
720  * Win~XP. Another name for v1.6's grayscale rendering is `font
721  * smoothing', and `Color ClearType' is sometimes also called `DWrite
722  * ClearType'. To differentiate between today's Color ClearType and the
723  * earlier ClearType variant with B/W rendering along the vertical axis,
724  * the latter is sometimes called `GDI ClearType'.
725  *
726  * `Normal' and `high' sampling describe the (virtual) resolution to
727  * access the rasterized outline after the hinting process. `Normal'
728  * means 1 sample per grid line (i.e., B/W). In the current Microsoft
729  * implementation, `high' means an extra virtual resolution of 16x16 (or
730  * 16x1) grid lines per pixel for bytecode instructions like `MIRP'.
731  * After hinting, these 16 grid lines are mapped to 6x5 (or 6x1) grid
732  * lines for color filtering if Color ClearType is activated.
733  *
734  * Note that `Gray ClearType' is essentially the same as v1.6's
735  * grayscale rendering. However, the GETINFO instruction handles it
736  * differently: v1.6 returns bit~12 (hinting for grayscale), while v2.1
737  * returns bits~13 (hinting for ClearType), 18 (symmetrical smoothing),
738  * and~19 (Gray ClearType). Also, this mode respects bits 2 and~3 for
739  * the version~1 gasp table exclusively (like Color ClearType), while
740  * v1.6 only respects the values of version~0 (bits 0 and~1).
741  *
742  * Keep in mind that the features of the above interpreter versions
743  * might not map exactly to FreeType features or behavior because it is
744  * a fundamentally different library with different internals.
745  *
746  */
747 #define TT_INTERPRETER_VERSION_35 35
748 #define TT_INTERPRETER_VERSION_38 38
749 #define TT_INTERPRETER_VERSION_40 40
750 
751 
752  /**************************************************************************
753  *
754  * @property:
755  * interpreter-version
756  *
757  * @description:
758  * Currently, three versions are available, two representing the
759  * bytecode interpreter with subpixel hinting support (old `Infinality'
760  * code and new stripped-down and higher performance `minimal' code) and
761  * one without, respectively. The default is subpixel support if
762  * TT_CONFIG_OPTION_SUBPIXEL_HINTING is defined, and no subpixel support
763  * otherwise (since it isn't available then).
764  *
765  * If subpixel hinting is on, many TrueType bytecode instructions behave
766  * differently compared to B/W or grayscale rendering (except if `native
767  * ClearType' is selected by the font). Microsoft's main idea is to
768  * render at a much increased horizontal resolution, then sampling down
769  * the created output to subpixel precision. However, many older fonts
770  * are not suited to this and must be specially taken care of by
771  * applying (hardcoded) tweaks in Microsoft's interpreter.
772  *
773  * Details on subpixel hinting and some of the necessary tweaks can be
774  * found in Greg Hitchcock's whitepaper at
775  * `https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'.
776  * Note that FreeType currently doesn't really `subpixel hint' (6x1, 6x2,
777  * or 6x5 supersampling) like discussed in the paper. Depending on the
778  * chosen interpreter, it simply ignores instructions on vertical stems
779  * to arrive at very similar results.
780  *
781  * The following example code demonstrates how to deactivate subpixel
782  * hinting (omitting the error handling).
783  *
784  * {
785  * FT_Library library;
786  * FT_Face face;
787  * FT_UInt interpreter_version = TT_INTERPRETER_VERSION_35;
788  *
789  *
790  * FT_Init_FreeType( &library );
791  *
792  * FT_Property_Set( library, "truetype",
793  * "interpreter-version",
794  * &interpreter_version );
795  * }
796  *
797  * @note:
798  * This property can be used with @FT_Property_Get also.
799  *
800  * This property can be set via the `FREETYPE_PROPERTIES' environment
801  * variable (using values `35', `38', or `40').
802  *
803  * @since:
804  * 2.5
805  */
806 
807 
808  /**************************************************************************
809  *
810  * @property:
811  * glyph-to-script-map
812  *
813  * @description:
814  * *Experimental* *only*
815  *
816  * The auto-hinter provides various script modules to hint glyphs.
817  * Examples of supported scripts are Latin or CJK. Before a glyph is
818  * auto-hinted, the Unicode character map of the font gets examined, and
819  * the script is then determined based on Unicode character ranges, see
820  * below.
821  *
822  * OpenType fonts, however, often provide much more glyphs than
823  * character codes (small caps, superscripts, ligatures, swashes, etc.),
824  * to be controlled by so-called `features'. Handling OpenType features
825  * can be quite complicated and thus needs a separate library on top of
826  * FreeType.
827  *
828  * The mapping between glyph indices and scripts (in the auto-hinter
829  * sense, see the @FT_AUTOHINTER_SCRIPT_XXX values) is stored as an
830  * array with `num_glyphs' elements, as found in the font's @FT_Face
831  * structure. The `glyph-to-script-map' property returns a pointer to
832  * this array, which can be modified as needed. Note that the
833  * modification should happen before the first glyph gets processed by
834  * the auto-hinter so that the global analysis of the font shapes
835  * actually uses the modified mapping.
836  *
837  * The following example code demonstrates how to access it (omitting
838  * the error handling).
839  *
840  * {
841  * FT_Library library;
842  * FT_Face face;
843  * FT_Prop_GlyphToScriptMap prop;
844  *
845  *
846  * FT_Init_FreeType( &library );
847  * FT_New_Face( library, "foo.ttf", 0, &face );
848  *
849  * prop.face = face;
850  *
851  * FT_Property_Get( library, "autofitter",
852  * "glyph-to-script-map", &prop );
853  *
854  * // adjust `prop.map' as needed right here
855  *
856  * FT_Load_Glyph( face, ..., FT_LOAD_FORCE_AUTOHINT );
857  * }
858  *
859  * @since:
860  * 2.4.11
861  *
862  */
863 
864 
865  /**************************************************************************
866  *
867  * @enum:
868  * FT_AUTOHINTER_SCRIPT_XXX
869  *
870  * @description:
871  * *Experimental* *only*
872  *
873  * A list of constants used for the @glyph-to-script-map property to
874  * specify the script submodule the auto-hinter should use for hinting a
875  * particular glyph.
876  *
877  * @values:
878  * FT_AUTOHINTER_SCRIPT_NONE ::
879  * Don't auto-hint this glyph.
880  *
881  * FT_AUTOHINTER_SCRIPT_LATIN ::
882  * Apply the latin auto-hinter. For the auto-hinter, `latin' is a
883  * very broad term, including Cyrillic and Greek also since characters
884  * from those scripts share the same design constraints.
885  *
886  * By default, characters from the following Unicode ranges are
887  * assigned to this submodule.
888  *
889  * {
890  * U+0020 - U+007F // Basic Latin (no control characters)
891  * U+00A0 - U+00FF // Latin-1 Supplement (no control characters)
892  * U+0100 - U+017F // Latin Extended-A
893  * U+0180 - U+024F // Latin Extended-B
894  * U+0250 - U+02AF // IPA Extensions
895  * U+02B0 - U+02FF // Spacing Modifier Letters
896  * U+0300 - U+036F // Combining Diacritical Marks
897  * U+0370 - U+03FF // Greek and Coptic
898  * U+0400 - U+04FF // Cyrillic
899  * U+0500 - U+052F // Cyrillic Supplement
900  * U+1D00 - U+1D7F // Phonetic Extensions
901  * U+1D80 - U+1DBF // Phonetic Extensions Supplement
902  * U+1DC0 - U+1DFF // Combining Diacritical Marks Supplement
903  * U+1E00 - U+1EFF // Latin Extended Additional
904  * U+1F00 - U+1FFF // Greek Extended
905  * U+2000 - U+206F // General Punctuation
906  * U+2070 - U+209F // Superscripts and Subscripts
907  * U+20A0 - U+20CF // Currency Symbols
908  * U+2150 - U+218F // Number Forms
909  * U+2460 - U+24FF // Enclosed Alphanumerics
910  * U+2C60 - U+2C7F // Latin Extended-C
911  * U+2DE0 - U+2DFF // Cyrillic Extended-A
912  * U+2E00 - U+2E7F // Supplemental Punctuation
913  * U+A640 - U+A69F // Cyrillic Extended-B
914  * U+A720 - U+A7FF // Latin Extended-D
915  * U+FB00 - U+FB06 // Alphab. Present. Forms (Latin Ligatures)
916  * U+1D400 - U+1D7FF // Mathematical Alphanumeric Symbols
917  * U+1F100 - U+1F1FF // Enclosed Alphanumeric Supplement
918  * }
919  *
920  * FT_AUTOHINTER_SCRIPT_CJK ::
921  * Apply the CJK auto-hinter, covering Chinese, Japanese, Korean, old
922  * Vietnamese, and some other scripts.
923  *
924  * By default, characters from the following Unicode ranges are
925  * assigned to this submodule.
926  *
927  * {
928  * U+1100 - U+11FF // Hangul Jamo
929  * U+2E80 - U+2EFF // CJK Radicals Supplement
930  * U+2F00 - U+2FDF // Kangxi Radicals
931  * U+2FF0 - U+2FFF // Ideographic Description Characters
932  * U+3000 - U+303F // CJK Symbols and Punctuation
933  * U+3040 - U+309F // Hiragana
934  * U+30A0 - U+30FF // Katakana
935  * U+3100 - U+312F // Bopomofo
936  * U+3130 - U+318F // Hangul Compatibility Jamo
937  * U+3190 - U+319F // Kanbun
938  * U+31A0 - U+31BF // Bopomofo Extended
939  * U+31C0 - U+31EF // CJK Strokes
940  * U+31F0 - U+31FF // Katakana Phonetic Extensions
941  * U+3200 - U+32FF // Enclosed CJK Letters and Months
942  * U+3300 - U+33FF // CJK Compatibility
943  * U+3400 - U+4DBF // CJK Unified Ideographs Extension A
944  * U+4DC0 - U+4DFF // Yijing Hexagram Symbols
945  * U+4E00 - U+9FFF // CJK Unified Ideographs
946  * U+A960 - U+A97F // Hangul Jamo Extended-A
947  * U+AC00 - U+D7AF // Hangul Syllables
948  * U+D7B0 - U+D7FF // Hangul Jamo Extended-B
949  * U+F900 - U+FAFF // CJK Compatibility Ideographs
950  * U+FE10 - U+FE1F // Vertical forms
951  * U+FE30 - U+FE4F // CJK Compatibility Forms
952  * U+FF00 - U+FFEF // Halfwidth and Fullwidth Forms
953  * U+1B000 - U+1B0FF // Kana Supplement
954  * U+1D300 - U+1D35F // Tai Xuan Hing Symbols
955  * U+1F200 - U+1F2FF // Enclosed Ideographic Supplement
956  * U+20000 - U+2A6DF // CJK Unified Ideographs Extension B
957  * U+2A700 - U+2B73F // CJK Unified Ideographs Extension C
958  * U+2B740 - U+2B81F // CJK Unified Ideographs Extension D
959  * U+2F800 - U+2FA1F // CJK Compatibility Ideographs Supplement
960  * }
961  *
962  * FT_AUTOHINTER_SCRIPT_INDIC ::
963  * Apply the indic auto-hinter, covering all major scripts from the
964  * Indian sub-continent and some other related scripts like Thai, Lao,
965  * or Tibetan.
966  *
967  * By default, characters from the following Unicode ranges are
968  * assigned to this submodule.
969  *
970  * {
971  * U+0900 - U+0DFF // Indic Range
972  * U+0F00 - U+0FFF // Tibetan
973  * U+1900 - U+194F // Limbu
974  * U+1B80 - U+1BBF // Sundanese
975  * U+A800 - U+A82F // Syloti Nagri
976  * U+ABC0 - U+ABFF // Meetei Mayek
977  * U+11800 - U+118DF // Sharada
978  * }
979  *
980  * Note that currently Indic support is rudimentary only, missing blue
981  * zone support.
982  *
983  * @since:
984  * 2.4.11
985  *
986  */
987 #define FT_AUTOHINTER_SCRIPT_NONE 0
988 #define FT_AUTOHINTER_SCRIPT_LATIN 1
989 #define FT_AUTOHINTER_SCRIPT_CJK 2
990 #define FT_AUTOHINTER_SCRIPT_INDIC 3
991 
992 
993  /**************************************************************************
994  *
995  * @struct:
996  * FT_Prop_GlyphToScriptMap
997  *
998  * @description:
999  * *Experimental* *only*
1000  *
1001  * The data exchange structure for the @glyph-to-script-map property.
1002  *
1003  * @since:
1004  * 2.4.11
1005  *
1006  */
1008  {
1011 
1013 
1014 
1015  /**************************************************************************
1016  *
1017  * @property:
1018  * fallback-script
1019  *
1020  * @description:
1021  * *Experimental* *only*
1022  *
1023  * If no auto-hinter script module can be assigned to a glyph, a
1024  * fallback script gets assigned to it (see also the
1025  * @glyph-to-script-map property). By default, this is
1026  * @FT_AUTOHINTER_SCRIPT_CJK. Using the `fallback-script' property,
1027  * this fallback value can be changed.
1028  *
1029  * {
1030  * FT_Library library;
1031  * FT_UInt fallback_script = FT_AUTOHINTER_SCRIPT_NONE;
1032  *
1033  *
1034  * FT_Init_FreeType( &library );
1035  *
1036  * FT_Property_Set( library, "autofitter",
1037  * "fallback-script", &fallback_script );
1038  * }
1039  *
1040  * @note:
1041  * This property can be used with @FT_Property_Get also.
1042  *
1043  * It's important to use the right timing for changing this value: The
1044  * creation of the glyph-to-script map that eventually uses the
1045  * fallback script value gets triggered either by setting or reading a
1046  * face-specific property like @glyph-to-script-map, or by auto-hinting
1047  * any glyph from that face. In particular, if you have already created
1048  * an @FT_Face structure but not loaded any glyph (using the
1049  * auto-hinter), a change of the fallback script will affect this face.
1050  *
1051  * @since:
1052  * 2.4.11
1053  *
1054  */
1055 
1056 
1057  /**************************************************************************
1058  *
1059  * @property:
1060  * default-script
1061  *
1062  * @description:
1063  * *Experimental* *only*
1064  *
1065  * If FreeType gets compiled with FT_CONFIG_OPTION_USE_HARFBUZZ to make
1066  * the HarfBuzz library access OpenType features for getting better
1067  * glyph coverages, this property sets the (auto-fitter) script to be
1068  * used for the default (OpenType) script data of a font's GSUB table.
1069  * Features for the default script are intended for all scripts not
1070  * explicitly handled in GSUB; an example is a `dlig' feature,
1071  * containing the combination of the characters `T', `E', and `L' to
1072  * form a `TEL' ligature.
1073  *
1074  * By default, this is @FT_AUTOHINTER_SCRIPT_LATIN. Using the
1075  * `default-script' property, this default value can be changed.
1076  *
1077  * {
1078  * FT_Library library;
1079  * FT_UInt default_script = FT_AUTOHINTER_SCRIPT_NONE;
1080  *
1081  *
1082  * FT_Init_FreeType( &library );
1083  *
1084  * FT_Property_Set( library, "autofitter",
1085  * "default-script", &default_script );
1086  * }
1087  *
1088  * @note:
1089  * This property can be used with @FT_Property_Get also.
1090  *
1091  * It's important to use the right timing for changing this value: The
1092  * creation of the glyph-to-script map that eventually uses the
1093  * default script value gets triggered either by setting or reading a
1094  * face-specific property like @glyph-to-script-map, or by auto-hinting
1095  * any glyph from that face. In particular, if you have already created
1096  * an @FT_Face structure but not loaded any glyph (using the
1097  * auto-hinter), a change of the default script will affect this face.
1098  *
1099  * @since:
1100  * 2.5.3
1101  *
1102  */
1103 
1104 
1105  /**************************************************************************
1106  *
1107  * @property:
1108  * increase-x-height
1109  *
1110  * @description:
1111  * For ppem values in the range 6~<= ppem <= `increase-x-height', round
1112  * up the font's x~height much more often than normally. If the value
1113  * is set to~0, which is the default, this feature is switched off. Use
1114  * this property to improve the legibility of small font sizes if
1115  * necessary.
1116  *
1117  * {
1118  * FT_Library library;
1119  * FT_Face face;
1120  * FT_Prop_IncreaseXHeight prop;
1121  *
1122  *
1123  * FT_Init_FreeType( &library );
1124  * FT_New_Face( library, "foo.ttf", 0, &face );
1125  * FT_Set_Char_Size( face, 10 * 64, 0, 72, 0 );
1126  *
1127  * prop.face = face;
1128  * prop.limit = 14;
1129  *
1130  * FT_Property_Set( library, "autofitter",
1131  * "increase-x-height", &prop );
1132  * }
1133  *
1134  * @note:
1135  * This property can be used with @FT_Property_Get also.
1136  *
1137  * Set this value right after calling @FT_Set_Char_Size, but before
1138  * loading any glyph (using the auto-hinter).
1139  *
1140  * @since:
1141  * 2.4.11
1142  *
1143  */
1144 
1145 
1146  /**************************************************************************
1147  *
1148  * @struct:
1149  * FT_Prop_IncreaseXHeight
1150  *
1151  * @description:
1152  * The data exchange structure for the @increase-x-height property.
1153  *
1154  */
1156  {
1159 
1161 
1162 
1163  /**************************************************************************
1164  *
1165  * @property:
1166  * warping
1167  *
1168  * @description:
1169  * *Experimental* *only*
1170  *
1171  * If FreeType gets compiled with option AF_CONFIG_OPTION_USE_WARPER to
1172  * activate the warp hinting code in the auto-hinter, this property
1173  * switches warping on and off.
1174  *
1175  * Warping only works in `normal' auto-hinting mode replacing it.
1176  * The idea of the code is to slightly scale and shift a glyph along
1177  * the non-hinted dimension (which is usually the horizontal axis) so
1178  * that as much of its segments are aligned (more or less) to the grid.
1179  * To find out a glyph's optimal scaling and shifting value, various
1180  * parameter combinations are tried and scored.
1181  *
1182  * By default, warping is off. The example below shows how to switch on
1183  * warping (omitting the error handling).
1184  *
1185  * {
1186  * FT_Library library;
1187  * FT_Bool warping = 1;
1188  *
1189  *
1190  * FT_Init_FreeType( &library );
1191  *
1192  * FT_Property_Set( library, "autofitter",
1193  * "warping", &warping );
1194  * }
1195  *
1196  * @note:
1197  * This property can be used with @FT_Property_Get also.
1198  *
1199  * This property can be set via the `FREETYPE_PROPERTIES' environment
1200  * variable (using values 1 and 0 for `on' and `off', respectively).
1201  *
1202  * The warping code can also change advance widths. Have a look at the
1203  * `lsb_delta' and `rsb_delta' fields in the @FT_GlyphSlotRec structure
1204  * for details on improving inter-glyph distances while rendering.
1205  *
1206  * Since warping is a global property of the auto-hinter it is best to
1207  * change its value before rendering any face. Otherwise, you should
1208  * reload all faces that get auto-hinted in `normal' hinting mode.
1209  *
1210  * @since:
1211  * 2.6
1212  *
1213  */
1214 
1215 
1216  /* */
1217 
1218 
1220 
1221 
1222 #endif /* FTDRIVER_H_ */
1223 
1224 
1225 /* END */
#define FT_END_HEADER
Definition: ftheader.h:54
#define FT_BEGIN_HEADER
Definition: ftheader.h:36
struct FT_Prop_IncreaseXHeight_ FT_Prop_IncreaseXHeight
struct FT_Prop_GlyphToScriptMap_ FT_Prop_GlyphToScriptMap
unsigned int FT_UInt
Definition: fttypes.h:231
unsigned short FT_UShort
Definition: fttypes.h:209